tonight on "world news," trouble in the air. we learn of another american airlines flight with a row of loose passenger seats. american airlines says late today they think they know what happened, but why? should you book a flight? shootout. this morning, an american agent killed in a firefight near the mexican border. a massive manhunt under way from helicopters to horseback. fat chance. the people paid thousands of dollars by doctors to eat one fast food meal every day for months. what happened to their bodies? how much weight did they gain? and lucky charm. why the hopes and dreams of everyone in this superstitious city rest on this guy. why does he have to lose for them to win?

good evening. as we come on the air, we learned it has happened again. a third american airlines flight forced to land after a row of seats came unbolted. half of their fleet of 757s were grounded for inspection. most of them now back in service. but even so, there have been a flurry of cancellations and delays. so what do you do if you're booking a flight? and what is american airlines saying tonight about the clues they have found? abc's senior national correspondent jim avila tells us. >> reporter: boston's logan field, one of americans' boeing 757s, 47 of which, nearly half the fleet taken out of service overnight and into today as the troubled airline tries to make sure no more of its coach seats come loose in flight, as they have three separate times. >> seats 14 a, b, and c, i think, are totally disconnected.

>> somehow we introduced failure. we're not sure if it is a mechanical failure or a human failure. >> reporter: american saying today it has identified the problem -- because seats came loose. in one case, flipping passengers on their backs. the seats came in rows of three. the row is held to the floor with what is called a saddle clamp that was improperly installed on the planes where the seats disengaged. >> on the safety side of the situation, american's doing all that it can do right now to ensure that the seats are being looked at and installed as correctly as possible. >> reporter: american says the investigation is still underway, but so far the airline cannot give a solid answer as to why now. these seats have been in use for up to 20 years, and never come loose before. aviation sources say the last eyes and hands on the saddle clamps in all three loose

seat incidents belonged to company mechanics. leading to suspicions of possible sabotage. but safety experts tell abc news that would be a first. >> to deliberately think that somebody would do something to a seat track assembly to cause it to come loose in a flight is something that is not thought of in this industry. >> reporter: the mechanics union, which lost jobs to outsourcing, says it has had nothing to do with the loose seats and points to the new private maintenance. just the latest series of labor troubles for american airlines, which has suffered more than 2,200 delays and 75 cancellations. on time only 57% of the time over the last three days. more than double the delays for united and delta, which are both punctual 80% of the time. >> it's going to take american some time to rebuild trust in terms of the reliability of the schedule. >> reporter: american airlines says on the record it's ruled out sabotage. they believe the installation mistakes are the result of human or mechanical errors.

one interesting note, one of the seat rows that was loose was loose for six days worth of flights without being noticed. should you take an american airlines flight? >> that's the question. >> reporter: the experts are telling us if you can be flexible and don't have to be someplace on time, it's okay. that it's safe, just not very dependable as far as on time. >> back on the story tonight. thanks, jim. we turn now to a manhunt under way at this hour in arizona. helicopters and horses in pursuit along a dangerous stretch of the mexican border. this morning, a shootout left one american border agent dead, another wounded. the agent who died, 30-year-old nicholas ivy. and the question tonight, was this a mexican drug cartel in action? cecilia vega joins us from the border there. >> reporter: diane, good evening to you. let me just show you how close we're talking. that mountain right over my

shoulder, that is the other side of the border. that is mexico. this area has earned the nickname cocaine alley. it's considered to be one of the most popular places for illegal entries all along the border. today for the agents at this station, this is a place of mourning. it is remote, dangerous, and deadly. and it was here, early this morning on this dusty stretch of land where arizona meets mexico that three border patrol agents were fired on. one made it out safely. another was shot twice and expected to recover. the third agent, 30-year-old nicholas ivy, was shot dead. >> we suspect this is probably some type of narcotics trafficking event that these agents encountered. but at this time, that would be speculative. >> reporter: it was just before 2:00 in the morning when something triggered one of the many motion sensors on the border. this is how this advanced technology works. sensors buried below ground automatically alert the nearest border patrol office.

there's one right over there. when they detect a certain weight, whether it's a smuggler, an illegal crosser, or a large animal, border patrol agents have to come out and investigate. the three agents headed three miles north of the border. as they headed up a hill, someone fired right at them in what is being described as an ambush. the agents work in the very station in arizona named just two weeks ago for brian terry, the last board patrol agent fatally shot on duty. his 2010 death from a firearm sold through the notorious fast and furious operation ignited a fire storm. it's unknown if the weapon that killed ivy has a link to that controversy. it's clear how dangerous life can be. >> agent ivy died in the line of duty. protecting our nation against those who threaten our way of life. his death only strengthens our resolve.

>> reporter: and this terrain out here, so rough that agents are still processing the crime scene. they say it could take a couple of days. now you can see the flags here at this station lowered today. agents have been saying this has given them a resolve to make this a safer place. diane? >> all right, cecilia vega, thanks so much tonight. now we turn to countdown to the first big debate. 24 hours until the candidates face each other on the stage. president barack obama and governor mitt romney both in marathon training sessions. their wives and running mates carrying the banners today with mixed results. 35 days to go. "your voice, your vote." our political team is back. abc's jake tapper and abc's david muir inside the debate hall right now. covering it all. jake starts us off. >> reporter: good evening, diane. the two candidates largely kept to themselves today. leaving the hard work of campaigning to their surrogates. who hit the campaign trail in a fever pitch.

not always staying on message. in battleground state north carolina, the vice president tried to assail the republican ticket, but he did so in way that brought fire upon himself. >> how they can justify raising taxes on the middle class that's been buried the last four years. >> reporter: paul ryan pounced. >> vice president biden, just today, said that the middle class over the last four years has been, quote, buried. we agree. that means we need to stop digging by electing mitt romney as the next president of the united states. [ applause ] >> reporter: the vice president later said that the middle class pain was due to bush policies. that romney and ryan want to repeat. the debate symbolizes a problem for the president. even though the economic collapse happened under bush, four years later, families are still hurting. many in the middle class are barely treading water. all guaranteed fodder for tomorrow night's debate in denver. the first lady is making her way there.

first stop in ohio. >> are you fired up? >> reporter: where early voting began today. >> are we going sit back and watch everything we worked for and fought for to just slip away? >> reporter: ann romney got to colorado before her. >> we have a debate coming up. we're excited about that. we're focused. >> reporter: family members' nerves are on edge, as josh romney confided to diane in august. >> i hate the debates. trying to sit there and be cool and keep a smile on your face. inside you want to fall down. >> reporter: four years ago, michelle obama would get so nervous during the debates she didn't like to watch them. she'll be there tomorrow in the debate hall. we turn to david muir who is there. david? >> reporter: hey, jake. i'll see you right here in the debate hall tomorrow night. tonight, here are some key decisions made moments ago. a coin toss between the campaigns determining that president obama will be introduced first and will have the first question.

governor romney will get the final argument. there was even a toss about which of the wives will be introduced first. ann romney will be introduced first. i want to show the debate stage. both podiums. both candidates will stand with one another. that's why the romney team is concentrating on the answers and the body language. where was he earlier today? take a look at the pictures that came in. at chipotle. getting in line with senator rob portman who has been playing president obama in mock debates. taking pictures with some of the workers there. we asked the supporters what they would say if they were coaching him in the mock debates? if you were inside that debate prep room, what would you tell the governor? >> be honest. be straightforward. >> reporter: what do you tell him in the debate room? >> i say show them who you are. there's been bad press because of his comments about the 47% of the 49% that he doesn't care about. he does care about everyone.

>> i would say use all the facts that you can and speak from the heart. >> reporter: she said show some heart on this stage. i did talk with a campaign adviser today. he said there's no question that the 47% will come up on the debate stage. they've been training the governor on that. whether it is from the moderator or an answer from president obama. one other thing i heard today is that governor romney does not have to win a charm offensive. on that debate stage. he has to prove he can relate to average american problems. a lot at stake here tomorrow night. >> love the citizen debate coaches, david. and as everybody knows, you and jake and george stephanopoulos, the entire political team will be covering it all tomorrow night. please join us wednesday night. one on one, the candidates debate. 9:00 p.m. eastern, 6:00 pacific. now the peanut butter recall. we've been reading all your posts and e-mails to us about peanut butter and which brands are linked to at least 30 cases

of salmonella poisoning. so many of you are asking us as we go through our kitchen cabinets, what should we do? steve osunsami has a user's guide for families. >> reporter: today, government official trying to contain this salmonella outbreak told us it doesn't look good and to expect more reported cases linked to jars of peanut butter sold at grocery stores across the country. so far, 30 people sick, most of them children, across 19 states. for families searching through kitchen cabinets tonight for potentially dangerous jars of nut butter, it's confusing. first, what jars and brands are being recalled? well, it isn't your larger name brands like jif or skippy. those products are fine. all of the recalled products are linked to the sunland peanut butter corporation in new mexico they make peanut butter under many labels. sunland, trader joe's, sprouts, and the archer farms brand sold at target. >> all the illnesses that have been investigated are related to

the peanut butter products from the one plant. >> reporter: so now you've found one of these brands in your cupboard. should you automatically toss it out? the company says to look on the side of the jar for the "best if used by" date. anything between may 1st and september 24, 2013, throw it away. what if your family has gone through half the jar? what are the signs of a salmonella infection? doctors say high fever, stomach cramps and dysentery, which can show up within one to three days. we talked with families of children who got sick. they tell us stories of 103-degree fevers that lasted for days. they were shocked to know it could have been their peanut butter. steve osunsami, abc news, atlanta. >> thanks so much to steve tonight. still ahead on "world news," imagine being paid thousands of dollars to eat fast food every single day. like this. the big experiment is under way tonight. we'll tell you why.

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have already learned so far. >> reporter: hitting the fast food drive-in for science. >> can i get five soft tacos. >> can i get two sausage burritos? can i get a number four? >> reporter: over and over and over again. it's been dave giocolo's life the past three months or so. as has been eating the food. a precisely measured 1,000 calories a day -- an extra meal daily -- fast food only. how many calories? >> 770. >> reporter: why? because this man is paying him to. dr. samuel klein is a researcher at washington university medical school in st. louis, trying to understand why weight gain leads to diabetes and hypertension. and how that relates to levels of fat in the liver and muscles. at some point, research on rats alone just isn't enough. somebody has to eat this food this way to -- >> ultimately, it has to come to people. >> reporter: and a radio ad -- >> attention overweight volunteers -- >> reporter: -- that offered a cash incentive, up to $3,500. depending on how long it would take. >> once i got into work, i called them right away. >> reporter: so did nurse dawn

freeman. >> it probably took a month to just get -- >> reporter: to get approved, to get accepted? >> to get approved. >> reporter: and so they ate. every day -- from one of these five restaurants. until their weight went up a target of 5% or 6%. dawn, in eight weeks went from 170 to 186. doesn't look like a lot. but here's how it felt. >> for two weeks it was all right, and then i started really feeling awful. i couldn't hardly breathe anymore. >> reporter: same thing for dave. because he learned, weight is mysterious. it doesn't go up in a straight line at all. he actually lost one week. it took him three months to put on 18 pounds. and, near the end -- you just want this thing to be over. >> yeah, i'm done with it now. i'm done with it. >> reporter: down the road, this research may help find therapies for obesity-related diseases. dave will have to take the weight off. that is what he needs complete to get his last $50. john donvan, abc news, st. louis. >> and you'll hear more of

john's report on "nightline." and coming up here, look closely. that is a dog stuck in the grille of a car. an indiana jones ride. how did she survive? the search is on for the miracle dog's owner. dog's owner. still make you take notice. there are a million reasons why. but your erectile dysfunction that could be a question of blood flow. cialis for daily use helps you be ready anytime the moment's right. you can be more confident in your ability to be ready. and the same cialis is the only daily ed tablet approved to treat ed and symptoms of bph, like needing to go frequently or urgently. tell your doctor about all your medical conditions and medications, and ask if your heart is healthy enough for sexual activity. do not take cialis if you take nitrates for chest pain, as this may cause an unsafe drop in blood pressure. do not drink alcohol in excess with cialis. side effects may include headache, upset stomach, delayed backache or muscle ache. to avoid long-term injury, seek immediate medical help for an erection lasting more than four hours.

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275 gallons of paint. in the next ten weeks, they'll strip the sign down to sheet metal and build it back up. you may remember the sign once read hollywoodland. by 1978, termites gnawed through the "o" and it rolled down the hill. hugh hefner auctioned off the l-a-n-d to pay for repairs. and so the sign became hollywood forever. and call her a cannonball poodle. a dog ran in front of a toyota camry and was catapulted into the front grille of car behind the license plate. for 11 miles it rode that way. a passing driver happened to think she saw some strange sight in the grille.

animal control workers wrangled the dog out. she lost a tooth. but no broken bones. everyone is now looking for her owner. coming up next, our correspondent goes head to head with teddy, the mascot who has to lose for his team to win. am to win. make 70,000 trades a second... ♪ reach one customer at a time? ♪ or help doctors turn billions of bytes of shared information... ♪ into a fifth anniversary of remission? ♪ whatever your business challenge, dell has the technology and services to help you solve it. prego?! but i've bought ragu for years. [ thinking ] wonder what other questionable choices i've made? i choose date number 2! whooo! [ sigh of relief ] [ male announcer ] choose taste. choose prego.

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and finally tonight, there's a very different kind of presidential race heating up in washington, d.c. this one is a foot race. and vying for victory, four men right off of mt. rushmore. that would be george, tom, abe, and, of course, teddy. jonathan karl tells us why washington is in a fever about all this. >> reporter: it's great times for baseball in the nation's capital. the hometown team heading to the major league playoffs for the first time since fdr was a white house rookie. but tough time for the nationals' favorite mascot. at every home game, teddy roosevelt races against tom, george, and abe. and every game for seven straight years, he's lost. he's faced -- hamstring problems. cheating competitors. rival mascots. even mr. kool-aid. he's also been disqualified --

illegal use of a segway. a zip line. a golf cart. some say it's a conspiracy against the republican roosevelt. >> i am outraged. that's why i'm calling for congressional hearings to right this horrible wrong. >> reporter: with the team finally winning, we set out to see if it was time for teddy to win, too. what's it going take to win? >> translator: you gotta run fast. >> reporter: after a little prerace workout, we put teddy to the test. come on, come on, come on. come on. he can run, all right, but there's something about that finish line. you had it! he just acts like a loser. despite never winning, teddy is the clear favorite with the fans. who do you think is going to win? >> all: teddy! teddy! >> reporter: what's your advice for teddy? >> don't fall! >> reporter: as the team celebrated, heading for the mlb playoffs, which begin this friday, we asked their big star,

michael morse, the big question. is teddy finally going to win that race? >> i hope. i hope he watches us and gets some encouragement. >> reporter: so as teddy raced last night, our hopes were high. teddy! close. oh, so close. teddy what happened? what happened, man? but maybe, just maybe, he needs to keep losing so they can win. jonathan karl, abc news, washington. >> and we thank you for watching. we're always here at abcnews.com. "nightline" of course lrks be here later. i'll see you tomorrow night. tonight from the city where almost anything goes a local lawmaker tells naked people to butt out of public place autos and hot, hotter. the bay area bakes and new record highs. i'll give you a look. >> also, here tonight a south bay city put police protection

up for bids. this will save a ton of money but so far no takers. >> and a bay area break through that could save millions of lives. researchers discovering a way for women to block the aids virus. >> take a look. live picture from the board walk. temperatures rose to 92 degrees today. not a record but unusually warm for this time of the year along the coast. and good evening, everyone. >> and and and there are triple digits this afternoon and it was hot today, again, as you know but that is going change tomorrow, today was a beach day. there are plenty of people taking in the sun. others relaxed, feeding the birds. and there is plenty of joggers out